1. Field of the Invention
The present invention relates to a method and a use of an aqueous, metal ion formate salt composition for reducing a residual water film on an interior of a pipeline during pipeline dewatering operations, which may involve the use of a pig or a plurality of pigs, for pipeline pressure testing operations, for freezing pointing suppression for sub-freezing temperature pipeline testing operations, i.e., operation at temperatures below 0° C.
More particularly, the present invention relates to a method and a use of an aqueous metal ion formate salt composition for pipeline operations. The method includes the step of contacting an interior of a pipeline with an effective amount of an aqueous metal ion formate salt composition, where the effective amount is sufficient to reduce substantially all or part of a residual water film from the interior of the pipeline during a dewatering operation. The metal ion formate salt composition includes a concentration of metal ion formate salt sufficient to dilute a water concentration of a residual film in a pipeline formed during a dewatering operation, where the dewatering operation may involve the use of a pig or multiple pigs. The present invention also relates to a method and a use of an aqueous metal ion formate salt composition in pipeline pressure testing operations. In sub-freezing point operations, the composition includes an amount of the metal ion formate salt sufficient to suppress a freezing point of fluid during repair and/or pressure testing operations to a desired temperature below a freezing point of ordinary water. The present invention also relates to a method and a use of an aqueous metal ion formate salt composition in all other sub-freezing temperature operations, including wet hydrocarbon transmission in sub-freezing temperature environments.
2. Description of the Related Art
Large volumes of methanol and glycol are routinely injected into gas transport pipelines to inhibit the formation of gas hydrates. These chemicals are derived from hydrocarbons and pose a potential environmental risk for the user. Companies commonly apply conditioning agents such as these for pipeline pre-commissioning operations.
Thermodynamic gas hydrate inhibitors are widely used for a number of applications. They essentially reduce the equilibrium temperature of hydrate formation by acting on the chemical potential of water in the aqueous phase. Chemicals such as methanol and glycol which fall into this category are generally dosed at relatively high concentrations (10-15% w/w) in the aqueous phase. Methanol is, on mass basis the most efficient of the conventional thermodynamic hydrate inhibitors. It is cheap and readily available, but it is a volatile chemical and losses of the inhibitor to the hydrocarbon phase can be considerable. In addition, the handling of methanol is complicated by its toxicity and flammability. While ethylene glycols are far less flammable, and their losses in the hydrocarbon phase are lower, they possess similar toxicity issues.
Despite the widespread use of brines in drilling fluids as gas hydrate inhibitors they are rarely used in pipelines. This is because conventional brines are corrosive, prone to crystallization and generally less effective than either methanol or glycol.
Pipelines that are used for transportation of hydrocarbon gases should be free of water. There are various reasons for this including: (1) prevention of hydrate formation, (1) prevention or reduction of corrosion, and (3) meeting gas sale specifications. Newly constructed pipelines are typically hydrotested; it is, therefore, necessary to dewater and condition the pipeline. This often involves the use of “conditioning” chemicals such as ethylene glycol or other similar glycols or methanol. These chemicals present the industry with certain toxicity problems, which prevents them from being discharged into marine environments. Further, methanol presents another problem; it is highly flammable in air.
Thus, there is a need in the art for an improved system and method for dewatering and conditioning pipelines and for a new fluid for use in repair and pressure testing at temperatures below the freezing point of pure water, which are environmentally friendly and have similar thermodynamic hydrate inhibition properties and similar freezing point suppressant properties compared to methanol and glycols.